On Tue, Nov 30, 2010 at 11:39:06AM +1100, Neil Brown wrote:
> Would it not be sufficient to simply gather flushes while a flush is pending.
> i.e
> - if no flush is pending, set the 'flush pending' flag, submit a flush,
> then clear the flag.
> - if a flush is pending, then wait for it to complete, and then submit a
> single flush on behalf of all pending flushes.
>
> That way when flush is fast, you do a flush every time, and when it is slow
> you gather multiple flushes together.
We can even optimize the second flush away if no other I/O has
completed since the first flush has started. That will always be the
case for SATA devices as the cache flush command is not queued.